The present invention relates to an apparatus and a method for delivering radiation to a sample and collecting radiation emanating from the sample and, in particular, where the sample is disposed in a deep well.
A deep well includes a cylindrical receptacle that is open at one end and closed at the opposite end with a membrane. Such a receptacle, or deep well, is useful where a volume of sample and reagent are to be mixed, and the resulting reaction products examined. An examination of the reaction products may be made in the wet state--before drawing the reagent/sample mixture through the membrane, or in the dry-state--after drawing the reagent/sample mixture through the membrane. If the latter, or dry-state, is chosen the membrane serves to filter out the reaction products, leaving them deposited on the surface of the membrane so as to be observed.
One type of examination that can be made of such a sample is an optical one. Optical examination takes advantage of the characteristic of certain analytical samples that, when illuminated by radiation of selected wavelengths, the sample will reflect the radiation or fluoresce in a manner indicative of its composition and/or concentration. This reflected or fluorescent radiation, sometimes referred to as the signal, can be collected and analyzed to provide information about the sample. In the absence of illumination, chemiluminescence radiation can also be collected and analyzed.
Typically, such an optical examination of a sample may be accomplished by a device such as the Dual-Wavelength Thin-Layer Chromato Scanner, Model CS-930 manufactured by the Shimadzu Corporation of Japan. Such devices include a radiation source, which is wavelength selectable, that is formed into an illumination beam and directed towards a sample. A portion of this illumination beam is re-directed to a monitoring photomultiplier to generate a reference signal while the remainder is directed to the sample. Part of the illumination radiation incident on the sample is reflected thereby to a reflection photomultiplier and a second part is transmitted through the sample to a transmission photomultiplier. The signals generated by the photomultipliers can then be analyzed to ascertain the presence and concentration of the chemical constituents of the sample.
Such analytical instruments of the prior art require expensive detectors due to the low collection efficiency of the illumination and detection system. This is due to the spatial relationships of the optical components. These component to air interfaces generate losses of radiation intensity which translate directly to losses of radiation delivered to a sample and signal returned therefrom. This problem is especially acute where samples are disposed in a deep well. Conventional analytical instruments cannot deliver excitation radiation to a point in, or in close proximity to, the sample since the optical components cannot fit within the deep well. Deep wells typically have a depth to diameter ratio greater than 3:1. Similarly, collection of radiation emanating from a sample must be done by such conventional instruments remotely, outside of the deep well.
Providing a bifurcated fiber optic bundle in the deep well to deliver radiation along one or more fibers and return radiation along the remainder of the fibers does not overcome the foregoing disadvantages.
In such a bifurcated bundle, a portion of the return signal is necessarily lost due to focusing inefficiencies and the fact that a portion of the bundle must be dedicated to delivering the illumination radiation, which is not useful for returning the signal. However, for that portion dedicated to returning radiation to a sensing apparatus, the fiber packing density is limited and a portion of the returning radiation will be incident on areas of the fiber optic bundle between individual fibers and, hence, lost.
A further disadvantage of such bifurcated bundles is their tendency to degrade if the epoxy holding the bundle together is subject to chemical attack by the sample or the reagent. In such a case, the bifurcated bundles cannot be cleaned, nor are they sufficiently inexpensive as to be disposable.